This invention relates to improved crank mechanisms adapted for use in any of numerous different types of apparatus in which it may be desired to convert a generally reciprocating type of motion to rotary motion, or vice versa, as for instance in driving a rotary shaft by a piston, or in driving a rotating wheel by pedals, as in a bicycle.
In a piston engine, the amount of horsepower produced by the engine is dependent in part upon the length of stroke of the piston or pistons, which in turn is determined by the effective radius of the crank throws to which the pistons are connected. In order to increase the output horsepower, it is desirable to lengthen the piston stroke and increase the crank radius. However, there have in the past been limits to the amount that the crank radius could be increased, since any such increase, besides lengthening the movement of the piston along its axis has had the associated adverse effect of correspondingly increasing the lateral movement of the crank throw and connecting rod end transversely of that axis. Excessive lateral movement of this type causes imposition of unwanted lateral forces by the piston against the cylinder wall, with rapid excessive wear of both of these parts, and in addition increases the size of the space which must be provided for reception of the crank shaft, and in general renders any increase in piston stroke beyond very narrow limits completely impractical. In a similar manner, the radius of a crank has been limited in other crank type mechanisms, as in a bicycle pedal assembly or other pedal actuated drive in which the length of the power stroke (downwardly in a bicycle) through which a user's foot can exert force through the crank mechanism cannot be increased without a corresponding unwanted increase in the front to rear motion of the foot.